Electronic and electrical devices are sensitive to contamination by liquids, in particular water, which can cause short circuiting between electronic or electrical components and corrosion on components such as circuit boards, electronic chips etc.
Portable, handheld and wearable devices are particularly at risk to damage from contamination by liquids, due to the high probability of them being exposed to environmental liquids, such as rain or steam from bathrooms. Handheld devices are particularly vulnerable to being accidentally splashed or dropped into liquid. In particular, electronic devices such as mobile phones, tablets, pagers, radios, hearing aids, laptops, notebooks, palmtop computers and personal digital assistants (PDAs) are all particularly at risk of being damaged by contamination with liquids.
In addition to electronic and electrical devices, it is desirable to apply coatings to a range of other products to enhance their performance. For example, the provision of liquid repellent coatings on laboratory equipment (such as pipette tips) has the advantage of minimising retention of reagents and thus increasing accuracy.
The use of plasma deposition techniques is known for the deposition of polymeric coatings onto a range of surfaces. This technique is recognized as being a clean, dry technique that generates little waste compared to conventional wet chemical methods. Using this method, plasmas are generated from organic molecules, which are subjected to an electrical field. When this is done in the presence of a substrate, the radicals of the compound in the plasma polymerize on the substrate. Conventional polymer synthesis will produce structures containing repeat units of the monomer species; whereas a polymer network generated using a plasma can be extremely fragmented, complex and irregular. The properties of the resultant coating can depend upon the nature of the substrate as well as the nature of the monomer used and conditions under which it is deposited.
Conventionally, a substrate to be coated is placed into a plasma chamber and the monomer is introduced into the chamber whilst the plasma is applied, resulting in a polymeric coating being mainly formed on the external surface of the substrate.
WO2005/021833 describes an apparatus for forming a coating via plasma polymerization in which the monomer is held in liquid form, for example in a syringe, and supplied into the plasma chamber via ultrasonic nozzles. Alternatively, the liquid monomer may be vaporized before entering the ultrasonic nozzles.
WO 2007/083122 describes a method of applying a polymer layer to electronic or electrical devices by plasma polymerisation in order to protect them from liquid damage. The polymer layer is applied either to the outer surface of a fully assembled device or an individual component. In both cases, the electronic or electrical device is placed in a plasma chamber along with the material to be deposited in the gaseous state.
Electronic or electrical devices typically comprise electronic and/or electrical components housed within an enclosure. The applicants have discovered that when treating fully assembled electronic or electrical devices by plasma polymerisation using prior art methods, the amount of coating on the internal surfaces of the electronic or electrical device (i.e. the internal surfaces of the enclosure and/or surfaces of the electronic and/or electrical components) is limited due to a lack of diffusion of the monomer into the device.
It is already known to treat the electronic and/or electrical components individually before assembling into the electronic or electrical device but this approach can interfere with the working of the phone due to the coating on the contacts or be unattractive and costly in mass manufacturing
Whilst much faster than wet chemistry techniques, prior art techniques of applying coatings by plasma polymerisation are currently too slow for them to be used ‘in-line’ during the manufacturing process of the electronic or electrical device. These prior art techniques require steps to ‘outgas’ the items being treated (i.e. drive off absorbed or trapped gases or vapours in the item) before coating, typically by exposing the item to reduced pressure within the chamber; these steps add significant time to the process. For example, a typical process time for treating an assembled mobile phone by prior art methods is 90 minutes per batch, which is too slow for the required takt time of <24 seconds required in the in-line process.